WASHINGTON — A new study of fetal exposure to BPA, a plastic additive found in some food packaging, shows that the chemical altered the mammary gland development in monkeys. The researchers reported that the changes they observed in the monkeys reinforce concerns that BPA – bisphenol A – could contribute to breast cancer in women.

The research was published on Monday in the Proceedings of the National Academy of Sciences.

For this study, the researchers fed pregnant rhesus macaques a piece of fruit containing BPA every day during their third trimester of pregnancy. The monkeys’ blood levels of BPA reached about the average level that BPA has been observed in human blood in the United States, said Patricia Hunt, a geneticist at Washington State University and one of the study’s authors.

After female offspring of these BPA-exposed monkeys were born, the researchers looked at their mammary glands. They found changes in the glands that give rise to dense tissue – something that in humans is a risk factor for breast cancer, Hunt said.

BPA is used mainly in polycarbonate plastics, such as those used for some kinds of food and drink packaging, and epoxy resins used in some food cans and other products. Scientists say it mainly enters the human body as a result of leaching from the packaging into food and drink.

Previous studies in mice have shown a correlation between changes in the mammary gland as a result of fetal BPA exposure and an increased risk of cancer later, as adults. The chemical industry argued that BPA-exposed mice might not be a good model for understanding the effects on humans, Hunt said. But the new study found the same results in primates, which are more similar to humans.

“This monkey study closes the gap between rodents and humans and suggests that we have much to fear from this chemical,” she said.

Earlier studies by Ana Soto and Carlos Sonnenschein, also authors of the new study, found that exposing rodents to small amounts of BPA could change their mammary gland development and lead to pre-cancerous and cancerous lesions when the animals exposed as fetuses became adults.

“We think that our results suggest that it is very likely that fetal exposure to BPA would also increase the propensity to develop mammary cancer in monkeys,” Soto said.

The sum of all the findings “strongly suggest that BPA is a breast carcinogen in humans and human exposure to BPA should be curtailed,” she said.

The Food and Drug Administration has said that BPA is safe. On March 30, the FDA rejected a petition by the Natural Resources Defense Council to ban it. The FDA then said that more studies were needed.

The American Chemistry Council said the new study was faulty and didn’t alter its view that BPA is safe. Other studies have convinced regulators in the U.S., Europe and Japan that BPA isn’t a carcinogenic hazard, said the council’s Steven Hentges.

“It’s hard to see the study’s relevance to humans, as only four or five animals were tested and the dose used was 10,000 times higher than typical human exposure to BPA, as documented by the Centers for Disease Control and Prevention’s large-scale biomonitoring studies,” Hentges said Monday in a written response when asked for comment about the study.

Hunt, however, said that researchers gave the monkeys the dose needed to reach levels in the monkeys’ blood that were similar to the amount of BPA in human bodies.

FDA spokesman Curtis Allen said the FDA would take the new report into consideration. “FDA has been studying and continues to study the effects of BPA and will make any necessary changes to BPA’s status based on the science,” he said.

The National Toxicology Program in 2008 found that studies showed reason for concern about the potential effects of current exposures of BPA on the brain, behavior and prostate gland of fetuses, infants and children. At the time, the National Toxicology Program, which is part of the Department of Health and Human Services, said that this concern level was in the middle _ the third level of a five-level scale of concern from serious to negligible. It reported minimal concern, the fourth level on the scale, for effects on the mammary gland and earlier puberty for females.